In a wireless communication system, in which an area to which wireless communication services are provided is divided into a plurality of zones (cells) around the base station, and which is configured of each base station and a plurality of terminals present in a cell that the base station covers, an interference problem that occurred in a boundary area (cell edge) of the cell has attracted attention. In a terminal in the cell edge, a distance difference between a distance from a base station in its local cell and a distance from a base station in an adjacent cell is small and reception powers of a desired signal reached from the local base station and an interference signal reached from the adjacent base station are similar, so a signal-to-interference power ratio is low and a communication rate or communication quality is degraded.
In order to solve the interference problem in the cell edge, various methods have been studied. These methods are roughly classified into two methods, that is, a method of avoiding interference and a method of using interference.
As the method of avoiding interference, Fractional Frequency Reuse (FFR) is typical. As described in PTL1, in this method, an local cell and an adjacent cell use different frequency ranges in a cell edge, so a desired signal received from an local base station and an interference signal reached from an adjacent base station are orthogonal in a frequency domain in a terminal in the cell edge, and thus it is possible to avoid interference. As described in NPL1, this method is considered for WiMAX that IEEE promotes standardization.
Meanwhile, as the method of using interference, an inter-base station cooperative transmission is one of typical methods. A plurality of base stations cooperate through a control station, and a transmission signal addressed to a terminal in a cell edge is simultaneously transmitted to the terminal not only from its local base station but also from a plurality of base stations, thereby it is possible to change a wave that was interference in the related art into a desired signal. As described in NPL2, with this method, standardization has been considered for long term evolution (LTE)-advanced by the 3rd generation partnership project (3GPP).
In the above two interference methods, differently from FFR, the inter-base station cooperative transmission transmits a desired signal of a terminal from a plurality of base stations including the local base station, thereby increasing reception power of the desired signal, while reducing interference. Therefore, it is expected that the inter-base station cooperative transmission can further improve the communication rate or the communication quality of the cell edge than FFR, and thus the inter-base station cooperative transmission attracts attention.